Electrical communication system



| KATCHATOUROFF ELECTRICAL COMMUNICATION SYSTEM XAZ l ZUUU 5 Sheets-Sheet 1 Filed Feb. 12, 1943 SUDU R95 2 N0 WIm, NW

m t m ATTORNEY KATCHATOUROFF ELECTRICAL COMMUNICATION SYSTEM Aug. 26,1947.

:5 sheets-sheet 2 Filed Feb. 12, 1943 lAlllAl INVENTOR Zia/v 4717246170019014 ATTORN EY Aug. 26, 1947. 1.. KA' I'CHATOUROFF ELECTRICALCOMMUNICATION SYSTEM 5 Sheets-Sheet 3 Filed Feb. 12, 1943 zoab EOdb f ni w AITORNEY Patented Aug. 26, 1947 UNITED STATES PATENT OFFICEELECTRICAL COMMUNICATION SYSTEM Application February 12, 1943, SerialNo. 475,687 In France October 27, 1941 11 Claims. 1

The present invention relates to electric communication systems ingeneral, and has reference in particular to systems in which telephoneand telegraph signals are transmitted over the same line.

More specifically, the invention relates to systerns in which. currentsof telephonic frequency are used for telegraph signals or the like,whereby at least one telephone conversation and one telegraphcommunication can take place simultaneously.

The term telegraph signals as used herein is intended to cover not onlytelegraph signals, in the strict sense of the word, but also remotecontrol signals, voice frequency calls and any other signalling, eitherby telegraphy or telephony or other methods of signal transmissionindependent of the latter two.

The general object of the present invention is to improve the operationof transmission systems of the above-mentioned type and assure gocdtransmission of telegraph and telephone signals over existing telephonecircuits that may be of inferior quality and particularly those thathave a low upper cut-off frequency.

With these and other objects in View, as will.

become more apparent hereinafter, the present invention is described indetail in the following specification, reference being had to theaccompanying drawings, in which- Fig. 1a shows frequency attenuationcurves ob tained from an existing transmission system of theabove-mentioned type;

Fig. 1b shows frequency attenuation curves for a system of the same typeas in Fig. 1a, but incorporating the improved features of the presentinvention;

Fig. 2 illustrates diagrammatically and in simplified form an embodimentof a receiver am plifier circuit for tele-printers constructed in theusual manner;

Figs. 3a and 31) show examples of signals cle formed by passage throughnarrow band filters applied to the circuit of Fig. 2;

Fig. 4 shows examples of the shapes of signals, amplified by the circuitaccording to Fig. 2, which act upon the motor relay of the tele-printerre-' ceiving apparatus after transmission over a variable attenuationline equipped with narrow band filters;

Fig. 5 shows diagrammatically an example of a simplified amplifierreceiving circuit for a teleprinter incorporating the features of theinvention;

Fig. 6 shows examples of the shapes of signals,

, reflections.

amplified by the circuit according to Fig. 5, which .act upon the motorrelay of the tele-printer receiving apparatus after transmission over 3.variable attenuation line equipped with narrow band filters.

Systems for the simultaneous transmission of telephone and telegraphsignals over aerial or underground telephone circuits comprising two orfour wires are known. The frequency band allotted to telegraphiccommunications is usually placed above the frequency band reserved fortelephony. For example, when existing lines of low cut-ofi frequency areused, the telephony frequency band A (Fig. 1a) is limited upwardly at1700 P. P, S. While the frequency band for telegraphy ranges from 1950to approximatel 2250 P. P. 6., as indicated by the letter B in Fig. la;the telegraphic communications contemplated in this instance beingtele-printer communications.

These systems present various disadvantages which are caused primarilyby the inappropriate choice of the carrier current frequency for thetelegraphic communications. In efiect, this frequency is placed in theextreme upper fringe of the transmission band. It should be clear thatin the end portions-of the frequency transmission band, the circuitspossess inferior transmission characteristics. In two-wire typecircuits, especially where frequencies adjacent the cut-off frequencyare used, rapid variation in the impedance is caused by the bandlimiting filters provided on the repeaters. This arrangement causes,insofar as telegraphic communications are concerned, circuit adaptationdefects and the appearance of The reflection scale varies rapidly, fromone frequency to another, about the carrier frequency and producesadditional distortions in the reception of signals. As a result, theoperation of the printing telegraph apparatus becomes unreliable forboth the distant reception of signals and the local control reception ofthe signals transmitted.

Moreover, in certain existing two-wire circuits, the Cut-off frequencyis set, as a matter of practice, below 2200?. P. S, in such cases, thetelegraph channel presents, aside from any questions of impedanceirregularities, a prohibitive attenuation, and operation of thetelegraph system is rendered impossible.

An object of the present invention is to provide means which willovercome these disadvantages.

I accomplish (these results in the following manner:

According to one feature of the present invention. the band fortelegraphy is placed in a position where the conditions for transmissionover the telephone line are more certain, namely, right within thetelephonic frequency band. To this end, a band is first of alleliminated from the telephonic transmission range of the system and thiseliminated band is then utilized for telegraphic transmission. Inpractice, it sufiices to place the telegraphic band in any desired spotof the band, between 500 and 1800 P. P. S. of the telephone frequencieswhich, it should be noted, will insure good transmission over any kindof telephone circuit. However, care should be taken lest the eliminationof such a band cause any appreciable loss of intelligibility intelephone conversations. Accordingly, the present invention fixes thecarrier current of the telegraphic communication in the center of theusual telephone frequency band of 500 to 2500 P. P. S., i. e., at 1500P. P. S.

For example, in simplified telephone and telegraph communicationsystems, where no intermediary relays are used, the frequenciestransmitted over the telephonic range run from 300 to 1250 P. P. S.(band C of Fig. 1b) and from 1750 P. P. S. up to the cut-01f frequencyof the lines used (band E, Fig. 1b). The band D, which transmitssuperimposed telegraph communications, has a value of about 300 P. P. S.and the separation obtained between the two channels amounts to 60 db.Such high value of the band of 300 P. P. S., which is lost fortelephony, may be reduced, however, to 200 P. P. S., if desired, byusing intermediate telegraph relays.

In such systems, the deformation of signals caused by the narrow bandfilters of the telegraph receiver necessitates a relatively preciseadjustment of the reception level, amounting to :25 db. In the absenceof such adjustment the drag of the received signals will produceinadmissible telegraphic distortions in the receiver amplifier. The needfor adjustment presents a great disadvantage especially in cases wheretelephone circuits of inferior quality (certain aerial circuits ortemporary hook-ups) are used. The difliculty which may arise in suchcircuits is that, even if the transmission is well adjusted, the signalswill be considerably distorted at the reception and the operation of thetale-printing apparatus rendered impossible by a variation in theattenuation of the line.

It is therefore a further objection of the invention to eliminate theneed for any and all adjustment and insure accurate operation of thetelegraphic apparatus even if the attenuation of the telephone circuitto which the apparatus is connected fluctuate within very wide limits,for example from to 30 db. The present invention accomplishes thisresult by means of an automatic adjusting device disposed in thereceiver amplifier of the tele-printing installation. This adjustingdevice consists of means for diminishing the amplification of the firststages by means of la. supplemental negative polarization created at themoment when the signal is received. The circuit, wherein thispolarization is created, is so arranged that polarization continues notonly during the length of the signal proper, but also during the passageof the signal drag. This adjusting device is particularly eiTective whenthe telephone line is traversed by no current and the so-called workingcondition of the line is the one that corresponds to a transmission ofcurrent at voice frequency.

With the aid of this adjusting device, it is possible to assure not onlyoperation of the system when the attenuation of the line circuit variesfrequently, but also easy starting of the apparatus. In other words,with this device it is always possible to obtain a connection of mediumquality by setting the two control attenuators at zero. Moreover,control reception is possible even if the mechanism especially used forthis purpose is not properly adjusted.

With reference to the drawings, Fig. 2 illustrates diagrammatically asimplified embodiment of a circuit for a tele-printer without automaticadjustment. The incoming signals traverse attenuator I and aretransmitted by transformers 2, 3 to grid 1 5 of first amplifier tube l.This first amplifier stage 4 is connected to a second amplifier-detectorstage 5. The output of the amplifierdetector stage 5 is connected to thecontrol grid of the direct current amplifier tube 6 Whose plate circuitincludes relay 7 of the tele-printer motor of the receiving station.When a deformed signal such as that shown in Fig. 3a is impressed uponthe grid of tube 4, a variation of the plate current of the output tube6 is produced after amplification and detection in tubes 4 and 5.

During non-operating periods, this plate current has a predeterminedvalue for example 24 mA. Upon reception of a signal, if its level issufficient, the plate current in question is nullified. Thereupon, themotor relay 1 of the teleprinting receiver, which is inserted in theplate circuit of last mentioned tube 6, is actuated.

If the level of the received signal, designated in in Fig. 3a, is justsufiicient to nullify the plate current of tube 6, the plate currentwill remain zero during a period of time substantially equal to theperiod of time 15 corresponding to the length of the signal proper. Aparasitic drag amplitude is created after the signal as a result of thepassage of the same across the narrow band filters. This parasitic dragamplitude, which has a lower value than to, is insufficient to reducethe plate current and hence incapable of actuating the relay.

If, on the other hand, the received signal is too strong, its valuebeing for example uz, as indicated in Fig. 3b, then the drag of thissignal would have a value us. This value us is sufficient toconsiderably reduce the current of tube 6 and oftentimes it may even besuificient to completely nullify said current. Relay 1 is then operatedby this drag in the same manner as if it were actuated by a usefulsignal. Relay 1 is released not just during the period 25 but duringperiod T which is substantially equal to the period 1. plus the durationof the parasitic drag. As a result, an inadmissible distortion of thesignals is created at the receiving station. The various graphs of Fig.4 represent the forms of the current received by the plate circuit oftube 5 When impulses of 20 ms. duration, separated by intervals of thesame duration, are transmitted from a distant point across a telephoneline equipped with narrow band filters. It will be noted that, when theattenuation of the line is 30 db. (attenuators such as element I of thereceiver and transmitter being eliminated), the received signals arevirtually undeformed. When the attenuation of the circuit is reduced,the received signals become stronger and stronger, the distortion of theduration increases and becomes practically prohibitive, while theprinting apparatus is rendered inoperative.

It is therefore a further object of the invention to provide suchamplifiers with corrective means which automatically assure an averagesignal length. An example of such corrective means according to thepresent invention is illustrated in the amplifier circuit according toFig. 5.

In this circuit, use is made of the fact that it is possible to suppressthe effect of signal drag, when the receiving level is too strong, byreducing the amplification of the stages 4 and '5. This reduction ofamplification may be accomplished by means of a supplemental negativepolarization. This supplemental negative polarization need be appliednot only during the length of the signal proper, but same must continuealso du ing t e p s ge of the dra i. e. it must last the period T,indicated in Fig. 3b. The amplification in the receiver, althoughreduced by this supplemental polarization, is nevertheless sulficient tonullify the plate current during period t (Fig. 3a). Thereafter, itbecomes so weak that the drag current cannot noticeably affect the platecurrent of the last stage.

According to one feature of the invention, the negative polarization inquestion is created automatically by the received signal itself. To thisend, the voice frequency tension taken off the plate circuit of thefirst tube 4 is applied simultaneously to the control grid 8 of thetriode D tion of tube 5 and to plate 9 of one of the diodes of this tube(which remains unused, or is not provided at all, in the circuitaccording to Fig. 2).

A rectifier circuit is inserted between this diode and the ground It.This rectifier circuit includes the dry rectifier H, for instance of thecopper oxide type, the condenser I2 and resistances l3 and Hi. A portionof the direct current of the diode traverses the rectifier H and chargescondenser l2. The rectifier is connected so as to be traversed. by thecharging current in direction of its lowest resistance. The values ofthe condenser lZ, of the resistance of rectifier H in the aforementioneddirection and of the resistances is and M are so adjusted that thecharging time of condenser I2 is of milli-second magnitude. The controlgrid it of amplifier tube 4, which is connected to condenser l2 acrossthe secondary Winding of input transformer 2, becomes polarized by thenegative tension produced at the terminals of resistanc l4. As a result,a reduction in the amplification of the first amplifier stage 4 occurs.This reduction is the greater, the highcr'the value of the negativesupplemental polarization is, i. e., the higher the value of thestrength of the received signal is. In order to obtain accurateadjustment both for signals that are but slightly stronger and thosethat are very much stronger, the present invention provides forauto-polarization of the second amplifier stage 5. This result isobtained in the following manner: A dry rectifier H, for instance acopper oxide rectifier, a condenser I8 and resistances I9 and 20 areinserted in the plate circuit it of the other diode which is normallyused (see Fig. 2). The negative tension obtained serves for the controlof the output tube 6 which acts as direct current amplifier. Thedirection of the rectifier connection i1 is arranged in the same manneras rectifier I l, except that this circuit is so adjusted as to have atime constant which is larger than that of the circuit of the firsttube. This arrangement eliminates blocking of the second stage beforethe increase of the first stage 4 has been reduced by the adjustment.Condenser I8 is connected to grid 8 of tube 5 across resistance 23. (InFig. 2 this connection is to the ground.)

When the received signal is discharged across the amplifier (at the endof period t), condensers l2 and [8 are discharged across rectifiers Hand H. However, at this time the rectifiers are traversed in a directionopposite to the charging direction and hence present a much higherresistance. As a result, the condensers become discharged much moreslowly than they are charged. Auto-polarization tensions of the twoamplifier stages 3 and 5, once they are set up, last for such a lengthof time that but slight amplification is produced during the passage ofthe signal drags. Thus, all possible influence of such drags upon themotor relay l of the printing apparatus is eliminated.

In rest position, while no signal is received at the receiver, the twofirst tubes are polarized only by the voltage drops produced by theplate currents traversing resistances 2| and 22, respectively. which areinserted between the cathodes and the ground it).

Fig, 6 illustrates various shapes of signals received by an apparatusincluding an automatic adjusting device such as described in connectionwith Fig. 5, these signals being transmitted under the same conditionsas those whose shapes, at the receiving station, are shown in Fig. 4. Itmay be noted that for attenuations from 0 to 30 db., the distortion ofthe length of the signal amounts to approximately 10%. In other words,it is possible to obtain accurate operation of the teleprinter systemfrom 0 to 30 db.

it should be noted that the present invention is not limited to theexact embodiments shown and described. but that on the contrary,numerous modifications and adaptations may be made without departingfrom the scope and spirit of the same.

I claim:

1. Method of simultaneous telegraph and telephone transmission over asingle channel, which includes transmitting telephone signals atfrequencies extending from the possible minimum to over 1200 cycles, andalso at frequencies extending from over 1700 cycles to the possiblemaximum, transmitting telegraph signals over a frequency band lyingbetween 1200 and 1700 cycles, amplifying received signals andsuppressing the effect of signal drag by temporarily reducing theamplification during the length of the signal proper and during thepassage of the signal drag.

2. The method of transmitting telegraph signals over a telephonetransmission channel which includes setting aside from the telephonicfrequency range a predetermined frequency band in the region near themean value of the telephonic frequency range, transmitting telegraphsignals over said set-aside frequency band, amplifying receivedtelegraph signals and suppressing the effect of signal drag bytemporarily reducing the amplification during the signal proper andduring the passage of the signal drag.

3. The method of simultaneous telegraph and telephone transmission overa single transmission channel which includes setting aside apredetermined frequency band in the region near the mean value of thetelephonic frequency range, and of relatively narrow range as contrastedwith the frequency range of the telephone signals transmitted,transmitting telegraph signals over said set-aside frequency band, andtransmitting telephone signals of frequencies both above and below saidset-aside band.

4. The method of simultaneous telegraph and telephone transmission overa single transmission channel which includes transmitting tele- 7 graphsignals in a frequency band within the limits of the telephone frequencyband and spaced from the edges thereof and simultaneously transmittingtelephone signals in the portions of the telephone frequency band aboveand below said telegraph signal band.

5. In a telephone system of predetermined bandwidth the method ofsimultaneous telegraph and telephone transmission over a singletransmission channel which includes transmitting telegraph signals in afrequency band Within the limits of said predetermined bandwidth andspaced from the ends thereof and simultaneously transmitting telephonesignals in the remaining portions of said bandwidth above and below saidfrequency band.

6. A system for simultaneous transmission of telegraph and telephonesignals over a single transmission system comprising means fortransmitting telegraph signals in a predetermined frequency band andmeans for simultaneously transmitting telephone signals at frequenciesabove and below said band.

7. A system for simultaneous transmission and reception of telegraph andtelephone signals over a single transmission system comprising means fortransmitting telegraph signals in a predetermined frequency band oversaid system and means for simultaneously transmitting telephone signalsat frequencie above and below said band over said system, means forreceiving said telegraph signals comprising means for eliminatingsignals outside of said band and means for receiving said telephonesignals comprising means for eliminating signal within said band.

8. A system according to claim 7 wherein said frequency band is nogreater than 300 cycles per second in width and is centeredsubstantially at 1500 cycles per second.

9. The method of transmitting telegraph signals over a telephonetransmission channel which includes transmitting telegraph signals in afrequency band within the limits of the telephone frequency band andspaced from the edges thereof, receiving and amplifying said signals andsuppressing the effect of signal drag by temporarily reducing theamplification during the signal proper and during the passage of thesignal drag,

10. A system for transmission of telegraph signals over a telephonetransmission channel com prising means for transmitting telegraphsignals in a frequency band within the limits of the telephone frequencyband and spaced from the edges thereof, means for receiving andamplifying said signals and mean for suppressing the effect of signaldrag comprising means for temporarily reducing the amplification of saidamplifying means during the signal proper and during the passage of thesignal drag.

11. A system for transmission and reception of telegraph signals over atelephone transmission channel comprising means for transmittingtelegraph signals in a frequency band Within the limits of the telephonefrequencies and spaced from the edges thereof, means for receiving andamplifying said signals, automatic volume control means to bring saidtelegraph signals to an appropriate level, said automatic volume controlmeans being prolonged in action whereby they act on the telegraph signaldrag as Well as on the signal proper and the amplitude of said drag isalways kept at a relatively low level with regard to the telegraphsignal proper.

LEON KATCHATOUROFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,323,880 Carnahan July 6, 19432,106,352 Kinkead Jan. 25, 1938 2,300,775 Cole et al. Nov. 3, 19422,121,287 Cowan June 21, 1938 2,332,494 Babcock Oct. 26, 1943 2,150,241Nichols Mar. 14, 1939 1,998,824 Steinberg Apr. 23, 1935

